Eight years after California Sen. Dianne Feinstein said the push for legalizing same-sex marriage was "too much, too fast, too soon," the Democratic Party will make history Tuesday when it is expected to be the first major party to endorse same-sex marriage in its platform.

While the plank packs no legal power, it marks a cultural milestone.

"Another important societal cue that things are shifting," said Amy Simon, an Oakland pollster who is working for advocates who are pushing to legalize same-sex marriage in Maine and Washington. "As people are working through their conflicting feelings on this, they're looking for cues, and this is another one."

The platform declaration could spark political blowback, and one of the nation's leading opponents of same-sex marriage already is trying to make it an issue in pivotal swing states that have passed laws codifying marriage as a union of one man and one woman.

"By doing this, the Democratic Party is basically telling voters in places like North Carolina and Florida that they're a bunch of bigots," said Sacramento consultant Frank Schubert, the strategist behind California's Proposition 8 and similar campaigns opposing gay unions in four states where marriage is on the ballot in November.

Support has grown

But analysts and pollsters say the issue is unlikely to be as volatile or powerful as it was in 2004, when 11 states put same-sex marriage bans on their ballots after then-San Francisco Mayor Gavin Newsom approved issuing wedding licenses to gay couples. Public support has grown since then, and now an average of 50 percent of Americans support same-sex marriage, according to the most recent polls.

But support in the polls has not translated into support at the ballot box. Voters have denied granting same-sex marriage rights 32 times when the issue was put before them. Voters in Maine, Maryland, Minnesota and Washington will decide the question this fall.

On Tuesday in Charlotte, delegates to the convention are also expected to support overturning the 1996 Defense of Marriage Act - signed by Wednesday night's keynote speaker, President Bill Clinton - which recognizes marriage only as between a man and a woman.

Democrats are trying to placate those with religious concerns: "We also support the freedom of churches and religious entities to decide how to administer marriage as a religious sacrament without government interference," a draft of the platform language states.

The party has come a long way in just four years, when it stopped short of endorsing gay nuptials, not wanting to contradict the stance of its nominee, then-Sen. Barack Obama. Obama said his views on the subject were "evolving."

Activists were so frustrated with Obama's position that some wore buttons saying "Evolve Already" at a White House reception last year for gay community leaders.

But when Obama expressed his full support for same-sex marriage in May, "that was a defining moment," said Rep. Barbara Lee, D-Oakland, a member of the party's platform committee. "It was a very clear political position that he supported marriage."

Tuesday's adoption of the platform, she said, "is a testament to (the lesbian, gay, bisexual and transgender) community, which would not give up."

As the Democrats prepare to endorse same-sex marriage, Republicans hardened their opposition to it at their convention in Tampa, Fla., last week.

In the platform approved at the GOP convention, Republicans vowed to uphold marriage between a man and a woman "as the national standard" and promote it "through laws governing marriage."

The GOP even sought to cast the issue in economic terms, saying "the future of marriage affects freedom. The lack of family formation not only leads to more government costs, but also to more government control over the lives of its citizens in all aspects."

Dissent stifled

When Margaret Hoover, a GOP strategist and CNN commentator, tried to get her party to soften its platform, National Organization for Marriage President Brian Brown described her position as "seditious" in a blog post Friday, deriding same-sex marriage supporters as "Margaret Hoover Republicans."

"This position really hurts the party with Millennial generation voters," Hoover said. "It helps codify feelings among younger voters, particularly, that the party is out of touch."

Hoover has helped to raise $1.8 million for American Unity PAC, which will support three pro-gay-rights Republicans this fall, including Rep. Mary Bono Mack, R-Palm Springs. Bono Mack has stopped short of endorsing same-sex marriage, saying only that it "is a states' rights issue."

GOP presidential nominee Mitt Romney's position on same-sex marriage has evolved in the opposite direction of Obama's.

Romney's pro-gay record

In a letter he wrote to the state chapter, Romney pitched his gay-friendly credentials: "I am more convinced than ever before that as we seek to establish full equality for America's gay and lesbian citizens, I will provide more effective leadership than my opponent.

"If we are to achieve the goals we share, we must make equality for gays and lesbians a mainstream concern. My opponent cannot do this. I can and will."

Now, Romney supports marriage only between a man and a woman - in tune with his party's platform.